Why malloc always does more than I asked for?

void *p = malloc(13); Almost all of us has seen this before when writing a safe c program. we know what this line does, atleast we know the purpose of it,
ask for 13 bytes, get 13 bytes
that’s what i thought when i started building this on a friday out of curiosity. 30 mins into it, without writing a single line of code… i knew that this almost never happens.